Amyloid P peptide (AP) 1-40 and AP 1-42 (Quality Controlled Biochemicals, Hopkington, MA) primarily FITC-labeled are being evaluated by electrospray (ESI) mass spectrometry and infrared (IR, Er-YAG laser, 2.94 pm) and ultraviolet (UV, nitrogen laser, 337 rim) matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for (1) purity, (2) size and polymerization state, and if needed for (3) oxidation state of methionine. Recent studies also indicate that it should be possible to use ESI MS to evaluate (4) ability to seed fibril formation and (5) length of time in culture medium prior to aggregation. Analyzed AP will be used to study passage of AP to the endothelial and smooth muscle cell layer and to monitor AP deposition using our novel blood brain barrier model system.